drm/amd/display: Add null check for 'afb' in amdgpu_dm_plane_handle_cursor_update (v2)

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Add null check for 'afb' in amdgpu_dm_plane_handle_cursor_update (v2) This commit adds a null check for the 'afb' variable in the amdgpu_dm_plane_handle_cursor_update function. Previously, 'afb' was assumed to be null, but was used later in the code without a null check. This could potentially lead to a null pointer dereference. Changes since v1: - Moved the null check for 'afb' to the line where 'afb' is used. (Alex) Fixes the below: drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm_plane.c:1298 amdgpu_dm_plane_handle_cursor_update() error: we previously assumed 'afb' could be null (see line 1252)

References

• https://git.kernel.org/stable/c/bd0e24e5e608ccb9fdda300bb974496d6d8cf57d
• https://git.kernel.org/stable/c/75839e2365b666ff4e1b9047e442cab138eac4f6
• https://git.kernel.org/stable/c/9132882eaae4d21d2fc5843b3308379a481ebdf0
• https://git.kernel.org/stable/c/e4e26cbe34d7c1c1db5fb7b3101573c29866439f
• https://git.kernel.org/stable/c/cd9e9e0852d501f169aa3bb34e4b413d2eb48c37